Attempts on 10.11.6 to use it give me unhelpful messages...
This is from a helper partition I mounted manually...
mkextunpack -v -d ~/BootOSXCache /Users/joconnor/BootOSX/com.apple.boot.R/System/Library/Caches/com.apple.kext.caches/Startup/kernelcache
Architecture i486 not found in mkext.
This is from my recovery partition...
Alaska:~ joconnor$ mkextunpack -v /Volumes/Recovery\ HD/com.apple.recovery.boot/prelinkedkernel
Bad mkext magic/signature.
Alaska:~ joconnor$ mkextunpack -v -a i486 /Volumes/Recovery\ HD/com.apple.recovery.boot/prelinkedkernel
Bad mkext magic/signature.
Alaska:~ joconnor$ mkextunpack -v -a x86_64 /Volumes/Recovery\ HD/com.apple.recovery.boot/prelinkedkernel
Bad mkext magic/signature.
Alaska:~ joconnor$ mkextunpack -v -d ~/BootOSXCache /Volumes/Recovery\ HD/com.apple.recovery.boot/prelinkedkernel
Bad mkext magic/signature.